The invention relates to an electronic ignition unit for triggering an active system, in particular restraint system, such as, for example, a seat-belt tensioner or airbag.
Such ignition units contain an ignition bridge in the form of, for example, a wire resistor or a film component and an ignition charge generally composed of a solid and which is in communication with the ignition bridge. In the event of the ignition unit being triggered, a current flows through the ignition bridge. The heat produced ignites the ignition charge, which, while expanding considerably, is converted into the gaseous state to produce a pressure that may be up to a few 100 bar. The gas can then enter a restraint system or the gas generator of an airbag or seat-belt tensioner through a predetermined breaking point in the housing of the ignition unit.
Such an ignition unit is described in DE 37 17 149, from which the preamble of claim 1 proceeds. The ignition unit has a solid housing through which contact pins for connection to a control line are brought out on the contact side. Formed on the opposite side of the housing is a cavity which contains the ignition charge and also the electronic ignition system connected to the contact pins. The electronic system is situated on a support that is securely disposed on the base of the cavity, while the ignition charge is disposed above the electrical system so that the gases produced after the ignition can escape upwards from the housing. During this process, the gases exert a force on the support element that may destroy the latter and, consequently, also the electronic ignition system.
Frequently, ignition units are operated on a bus system to which a plurality of ignition units is connected and on which the bus stations communicate bidirectionally. If the electronic ignition system of an individual ignition unit is destroyed during ignition, the communication on the bus may be interrupted so that the other stations can also no longer be activated.
The object of the invention is to provide an ignition unit in which the serviceability of the electronic ignition system is still given even after the triggering of the ignition element.
This object is achieved, according to the invention, by the support element and the electronic ignition system being at least partially covered with shock-absorbing material that reduces impact acting on the electronic ignition system during ignition.
The ignition unit has a housing that contains an ignition charge that is partly surrounded by a housing insert. The ignition charge is ignited by an ignition bridge that is disposed on a support element. Also situated on the support element is an electronic ignition system that is electrically connected to the ignition bridge and activates the latter. Electrically connected to the electronic ignition system is at least one contact pin that is led out of the housing in order to connect the ignition unit to an ignition line (bus). Alternatively, the ignition unit may also have sockets or other connecting elements.
The invention is based on the principle of covering the support element and the electronic ignition system disposed thereon at least partly with shock-absorbing material. The impact energy produced during the ignition of the ignition charge is dissipated by the shock-absorbing material before the pressure surge reaches the sensitive electronic ignition system. This ensures that the electronic ignition system functions even after the triggering of the ignition charge.
The shock-absorbing material may be disposed above the support element, i.e. between the support element and the ignition charge. In this case, the enveloping material cushions the impact energy generated by the ignition charge. The support element may be mounted in such a way that it yields as a result of bending to the pressure produced during the ignition.
The shock-absorbing material may also be disposed underneath the support element, i.e. on the side remote from the ignition charge. The pressure produced during the ignition then forces the support element downwards and, in this process, the shock-absorbing material underneath dissipates the energy. The two variants can be combined with one another.
Preferably, the support element and the electronic ignition system are surrounded by an envelope of shock-absorbing material, which envelope essentially only leaves the ignition bridge exposed. In this case, the cushioning at the top of the support element is achieved both by the housing insert and by the envelope. The envelope likewise undertakes the damping at the bottom of the support element. The hardnesses of the materials of the envelope and of the housing insert depend in this connection on the pressure to be expected and also on the sensitivity of the support element or the electronic ignition system disposed thereon. The ignition bridge is not covered by the envelope, but is in direct contact with the ignition charge. The pressure acting on the support element in the region of the ignition bridge has no adverse effects on the electrical conductors or electronic components since the latter are disposed completely inside the envelope. The pressure produced during the ignition is reduced by the deformation of the envelope or of the housing insert, with the result that the diminished pressure acting on the electronic ignition system does not damage the latter. The electronic components or conductors situated on the support element are therefore operational even after the ignition, with the result that clearly defined electrical states prevail between the contact pins. In addition, an electronic ignition system can issue items of information, for example about the state of the ignition unit, to a control computer even after triggering. This may be, for example, a status signal indicating that the ignition unit has been ignited. The bus line always remains undamaged, with the result that further ignition elements can be ignited.
In an advantageous embodiment of the invention, the cushioning properties of the material of the housing insert differ from those of the envelope. This two-stage structure makes possible improved, graduated pressure relief, it being possible, in addition, to cushion special pressure variations through the configuration of the interface between envelope and housing insert.
Preferably, the hardness of the material of the envelope is greater than that of the housing insert. This structure makes possible a good cushioning of the surge produced during the ignition process. In this case, the housing insert undertakes, to a certain extent, the function of a preliminary cushioning in which some of the pressure forces are already dissipated, while the remaining forces are reduced by the stiffer envelope. It is also possible for the housing insert to be composed of a harder material.
The support element may have a predetermined breaking point, and in this case no components or electrical conductors of the electronic ignition system are present in the region of the predetermined breaking point. In this way, excess energy can be reduced without the electronic ignition system being exposed to a dangerously increased pressure.
The electrical connection between the contact pins and the electronic ignition system disposed on the support element can be designed so as to be mechanically displaceable. This has the advantage that the support element can move during the ignition process independently of the contact pins, which permits small movements of the support element and, in addition, prevents the contact pins from being moved, which may result in damage to the ignition line plug connected to the contact pins. The connection between support element or the ignition bridge disposed thereon and the contact pins can be designed so that the support element has contact elements that are connected to the ignition bridge and that are applied to the contact pins, the support element being capable of displacement along the contact pins. During such movement, the contact elements remain continually in contact with the contact pins. The electronic ignition system of the support element may also be connected to the contact pins by flexible electrical conductors (bonding wire).